1. Field of the invention
The invention is directed in general to core plugs, and more particularly, to a core die apparatus for the formation of core plugs and an associated method of manufacturing a core plug.
2. Background of the invention
Core plugs, which include, among others, cup plugs, core hole plugs, freeze plugs and welsh plugs, have been known in the art. These are typically used to seal openings in, for example, automobile engines, transmissions, throttle body parts, water pumps, cylinder heads, and other housings. Generally, the core plug is slightly larger than the opening to be sealed, but also slightly softer. As such, when the plug is forced into the opening, a tight press-fit can be achieved which insures a proper mating of the surfaces of the plug to the opening, and, in turn, a leak-proof seal.
With many applications, such as with automobile engines, adhesive is utilized with the outer surface of the core plugs, further promoting the mating of the core plug to the opening, to, in turn, render better seal and reduce the risk of failure. Current manufacturing techniques apply a wet adhesive to either the opening or the smooth outer surface of the core plug. Subsequently, the core plug is forced into the opening. While such a method may achieve a solid bond between the core plug and the opening, the process is inefficient. First, a station must apply a wet adhesive to either the core plug or the opening. Next, a separate station forces the plug into the opening. As such, in the case of automobile engine assembly, the assembly line must stop at two stations. Inasmuch as factory output decreases every time the assembly line stops, two separate stations substantially affecting output, and, eliminating one station would be a significant improvement.
One improvement is disclosed in U.S. Pat. No. 4,750,457 issued to Bonutti. This reference discloses machining core plugs, to include grooves about their smooth outer circumferential surface. These grooves are then pre-filled with a dry-to-the-touch adhesive. This type of adhesive is activated, generally, by the absence of air. In the case of automobile engine assembly, these pre-filled core plugs are, at a single station, forced into the engine opening. Once forced into the opening, the adhesive becomes activated, and dries to form a solid leak-proof seal. While this method appears to reduce the engine assembly time by eliminating a station, there are other drawbacks associated with this process.
Specifically, the cost of machining grooves into the outer circumference of the core plug can be cost prohibitive. Indeed, machining of the core plug is labor intensive and time consuming. Additionally, to make a large volume of plugs, a multitude of expensive milling equipment is necessary. Accordingly, any savings realized by the elimination of a station is more than offset by the increased costs associated with the machined core plug. Notwithstanding the availability of this method, the auto manufacturers have continued to utilize the wet adhesive (two station) method, inasmuch as it appears to be less costly than the machined core plug.